1. Field of the Invention
Exemplary aspects of the present invention relate to an image forming apparatus and a guide therefor, and more particularly to an image forming apparatus and a guide for guiding a recording medium bearing a toner image from a transferor to a fixing unit.
2. Description of the Related Art
A related art image forming apparatus, such as a copying machine, a facsimile machine, a printer, or a multifunction printer having copying, printing, scanning, and facsimile functions, forms an electrostatic latent image on a photoconductor according to image data. The electrostatic latent image is developed with a developer (e.g., a toner) to form a toner image on the photoconductor. The toner image is transferred onto a recording medium (e.g., a sheet of paper) and sent to a fixing unit. In the fixing unit, a fixing roller and a pressing roller apply heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium.
The toner image formed on the photoconductor may be transferred onto the recording medium directly from the photoconductor or indirectly via an intermediate transfer medium (hereinafter referred to as the intermediate transfer belt). When the toner image is indirectly transferred via the intermediate transfer belt, the toner image formed on the photoconductor is transferred onto the intermediate transfer belt, and further transferred from the intermediate transfer belt onto the recording medium. The photoconductor or the intermediate transfer belt opposes a transfer bias roller to form a transfer nip at which the toner image is transferred from the photoconductor or the intermediate transfer belt onto one side (i.e., front side) of the recording medium. Specifically, the transfer bias roller applies a transfer bias having a polarity opposite to the polarity of a toner forming the toner image to the other side (i.e., backside) of the recording medium. Thus, the recording medium has an electric charge having the polarity opposite to the polarity of the toner and thereby attracts the toner, resulting in electrostatic transfer of the toner image.
When the amount of electric charge on the backside of the recording medium is too large, the recording medium is electrostatically attracted to the photoconductor or the intermediate transfer belt after the recording medium passes the transfer nip. In this case, a problem occurs such that the recording medium cannot separate from the photoconductor or the intermediate transfer belt, resulting in jamming of the recording medium. In addition, a problem which occurs is that the electric charge is abruptly transferred from the backside of the recording medium to a protruding member and/or a metallic member disposed on a downstream side from the transfer nip and on an upstream side from the fixing unit in a conveyance direction of the recording medium. This problem results in formation of a defective toner image, including small circle marks on the recording medium.
Further, when the backside of the recording medium has too large an amount of electric charge, the front side of the recording medium has a substantial amount of electric charge having a polarity opposite to the polarity of the electric charge of the backside of the recording medium. When the electric charge of the front side of the recording medium moves along the surface thereof, the toner image on the front side of the recording medium may be deformed. Specifically, a defective toner image (such as zigzag images) may be formed along a trail of the moving electric charge.
To address the above-described problems, an example of a related art image forming apparatus is proposed which further includes a discharger for discharging the backside of the recording medium immediately after the recording medium passes the transfer nip.
In addition, a related art image forming apparatus is provided which uses a spherical toner manufactured by a polymerization method so as to form a high resolution toner image. Toner particles of the spherical toner make point-contact with each other. Therefore, the toner particles attract each other with a decreased attracting force and have an increased flowability. The toner particles also make point-contact with the photoconductor or the intermediate transfer belt. Therefore, the photoconductor or the intermediate transfer belt attracts the toner particles with a decreased attracting force, thereby increasing transfer efficiency.
In the fixing unit, the fixing roller opposes the pressing roller to form a fixing nip at which the fixing roller and the pressing roller apply heat and pressure to the recording medium bearing the toner image so as to fix the toner image on the recording medium. When the fixing roller scrubs the pressing roller or the recording medium at the fixing nip, the fixing roller may be charged with the polarity opposite to the polarity of the toner by friction between the fixing roller and the pressing roller or the recording medium. When a recording medium bearing a toner image formed with a spherical toner is conveyed toward the fixing nip in a low temperature and low humidity environment, the toner on the recording medium may scatter in the moving direction of the recording medium immediately before the toner image reaches the fixing nip.
The related art image forming apparatus further includes a guide for guiding the recording medium bearing the toner image from the transfer nip toward the fixing unit. While the guide guides the recording medium, the recording medium scrubs the guide. Friction between the recording medium and the guide may charge the guide with the polarity opposite to the polarity of the toner and may charge the backside of the recording medium with the same polarity as that of the toner. The electric charge having the same polarity as that of the toner of the charged backside of the recording medium counteracts the electric charge having the polarity opposite to the polarity of the toner, i.e., the electric charge applied by the transfer bias roller. Thus, the backside of the recording medium has a decreased amount of electric charge having the polarity opposite to the polarity of the toner. This occurs easily in a low temperature and low humidity environment. The discharger also removes the electric charge from the backside of the recording medium. Thus, the recording medium electrostatically attracts the toner with a decreased attracting force. As a result, the above-mentioned toner scatter problem is caused.